In pressure-resistant containers for use in deep-sea research activities, in response to strong demands for strength enhancement and weight reduction, a titanium alloy or the like has been used as the material of construction of a pressure-resistant structure for deep-sea use purposes. Such a related art is disclosed in Patent Literature 1.
In this related art reference, there is described a titanium alloy-made pressure-resistant container composed of two head sections, each of which corresponds to a semispherical shell, and a barrel section having the shape of a right circular cylinder. In this pressure-resistant container, the barrel section has a flange formed at each end, and also each of the head sections has a flange formed at its opening edge. The sections are assembled into the container by joining the flanges together with bolts and nuts. The flanges of the barrel section, as well as the flanges of, respectively, the head sections, are each formed through the cutting operation of a forged product of a titanium alloy.
Furthermore, another related art is disclosed in Non-Patent Literature 1. In this related art reference, use of ceramics instead of a titanium alloy has been proposed, because, in the case where a pressure-resistant container is made of a titanium alloy as in the related art of the foregoing Patent Literature 1, the specific gravity of the pressure-resistant container increases as the resisting pressure depth increases, and the production cost also increases.
Meanwhile, in a pressure-resistant container for use in deep-sea research activities, in addition to strong demands for strength enhancement and weight reduction, there is a need to form a through hole in part of the shell of the pressure-resistant container for the placement of electronic equipment such as a camera inside the pressure-resistant container to check deep sea conditions, or for the attachment of a cable to effect remote operation.
As still another related art, in each of Patent Literatures 2 and 3, there is disclosed an example of formation of a through hole in part of a shell of a pressure-resistant container for use in deep-sea research activities. According to the related art described in Patent Literature 2, an underwater traveling body is provided with a pressure-resistant shell corresponding to a pressure-resistant container. The pressure-resistant shell has a through hole for the placement of an observation window.
According to the related art described in Patent Literature 3, an underwater exploratory apparatus comprises a container main body corresponding to a pressure-resistant container, a front-end flange, and a rear-end flange. The front-end flange and the rear-end flange have a through hole for the attachment of a cable, a driving shaft, and so forth.